In a stand mixer fitted with a paddle attachment, combine the flour, powdered sugar, and cold butter until the mixture resembles coarse crumbs.
Add the egg yolk and mix until the dough comes together. Wrap and refrigerate for at least 1 hour.
Roll the chilled dough onto a lightly floured surface into a thin circle. Transfer to a tart pan and press evenly into the bottom and sides. Trim excess dough. Freeze for 30 minutes.
Preheat the oven to 338°F (170°C). Prick the crust with a fork and bake for 20 minutes or until lightly golden. Let cool completely.
In a bowl, whisk together egg yolks, sugar, cornstarch, and vanilla extract until smooth.
Heat the milk and heavy cream in a saucepan over medium heat until warm but not boiling. Slowly pour into the egg mixture while whisking continuously.
Return the mixture to low heat and stir constantly until slightly thickened and silky.
Reduce the oven temperature to 302°F (150°C). Pour the custard filling into the cooled tart shell.
Bake for about 15 minutes or until the filling is set around the edges but slightly wobbly in the center.
Cool the tart completely, then refrigerate until fully chilled.
Before serving, sprinkle the top evenly with white sugar. Use a culinary torch to caramelize the sugar until golden brown and crisp.
Slice and serve chilled.